Cardiovascular Monitoring Electrocardiogram Dr.noha elsayed

Electrocardiography Electrical activity is recorded by electrocardiogram (ECG) P wave corresponds to depolarization of SA node QRS complex corresponds to ventricular depolarization T wave corresponds to ventricular repolarization Atrial repolarization record is masked by the larger QRS complex Cardiovascular System: Intrinsic Conduction System , Cardiovascular System

Electrocardiography Figure 18.16 Chapter 18, Cardiovascular System

Isoelectric line No electrical activity baseline

EKG Records 1. Amount of voltage generated by ht – vertical scale 2. Time required for voltage to travel thru ht – horizontal scale

ECG Interpretation What is your approach to reading an ECG? Rate Rhythm Axis P wave PR interval QRS complex QT interval ST segment – T wave SLIDE STARTS WITH QUESTION ONLY Ask interns about their method for interpreting an ECG. Emphasize the importance of interpreting an ECG always in the same order so that nothing is missed. Question will appear first in presentation, then answers.

EKG Interpretation: 8 criteria 1. What is the rate? Quick estimate: Count # R waves in a 6 second strip x 10 6 second strip = 3 “tic” marks Square Counting: 300-150-100-75-60-50-42A

Role of 300 Take the number of “big boxes”between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate Although fast, this method only works for regular rhythms.

10 Second Rule As most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms.

Rythm 2. Is rhythm regular or irregular? Measure distance between RR interval Measure throughout full 6 second strip

Axis 3.Left or right axis deviation? Look at limb leads I and aVF. Normal: I +, aVF + LAD: I +, aVF – RAD: I -, aVF + Left Axis Deviation (LAD) Right Axis Deviation (RAD)

Axis Deviation

QRS-axis

4-P Wave First component of a normal ECG Represents the spread of electrical activity over the atrium, atrial depolarization. The normal depolarization begins at the sinoatrial (SA) node near the top of the atrium. Because of the top-to-bottom, right-to-left path, the P wave is normally largest in Lead II Configuration: usually rounded and upright in all leads except R Amplitude is usually 2-3 mv in any lead

Are P waves present? Should be 1:1

Abnormal rhythms with P waves

5. What is the PR Interval? PRI

PR Interval Measured from the beginning of the P wave (atrial depolarization) to the beginning of the QRS complex (ventricular depolarization) Represents the time it takes for an impulse to travel from the SA node through the atria and the AV node Normally between 0.12 to 0.20 seconds in duration If prolonged, > 0.20 seconds indicates conduction delay through the AV node and is called a 1st degree AV block

6. What is the width of QRS complex? Normal QRS duration is 0.06 to 0.12 seconds

QRS Complex Represents activation of the ventricles, ventricular depolarization Special conducting bundles spread the wave of depolarization rapidly over the bundles May have one, two or all three components : Q R S Q wave is the first negative wave after the P wave and before the R wave. The Q wave represents activation of the ventricular septum R wave is the first positive wave after the P wave. Most of the ventricle is depolarized during the R wave. S wave is the negative wave after the R wave. Lengthening of the QRS indicates some blockage of the electrical conduction system either due to ischemia, necrosis of the conducting tissue, electrolyte imbalance or hypothermia

Sinus Rhythm Impulse originates in SA node (normal pacemaker site) Normal Sinus Rhythm - NSR Regularity – regular Rate - 60 – 100 / minute P waves = 1:1 PRI = .12 - .20 QRS = .12 or <

7-Q-T Interval QT interval represents total ventricular activity. It is the summation of ventricular depolarization to repolarization Can vary with heart rate Measured from the beginning of the Q wave to the end of the T wave Corrected QT interval (QTc) takes heart rate into account and provides various normal values based on the rates Rule of thumb – QT interval should be less than half the preceeding R-R interval The U wave represents repolarization of the Purkinje fibers but isn’t always seen on paper. A prominent U wave may be caused by hypercalcemia or hypokalemia

8.ST segment & T wave ST segment – Elevation or depression indicates ischemia. Figure on right: Concave– Normal  smile. Convex – MI  frown. T wave - can diagnosis ischemia, hyperkalemia Now we are ready to start an ECG. a case day is workable.

Normal Values - HR dependent, cave: long QT syndrome! PR interval: 0.12-0.21 s QRS complex: 0.06-0.1 s QT interval: < 0.44 s - HR dependent, cave: long QT syndrome! ST segment changes: - significant if > 1mm in limb leads, > 2mm in precordial leads Q waves: significant if > 1/3 of total QRS complex